Time-domain astronomy

Time-domain astronomy is the study of how astronomical objects change with time. Though the study may be said to begin with Galileo's Letters on Sunspots, the term now refers especially to variable objects beyond the Solar System. Changes over time may be due to movements or changes in the object itself. Common targets included are supernovae, pulsating stars, novas, flare stars, blazars and active galactic nuclei. Visible light time domain studies include OGLE, HAT-South, PanSTARRS, SkyMapper, ASAS, WASP, CRTS, GOTO and in a near future the LSST at the Vera C. Rubin Observatory.

Time-domain astronomy studies transient astronomical events, often shortened by astronomers to a transients as well as various types of variable stars, including periodic, quasi-periodic, and that of changing behavior or type. Other causes of time variability are asteroids, high proper motion stars, planetary transits and comets.

Transients characterize astronomical objects or phenomena whose duration of presentation may be from milliseconds to days, weeks, or even several years. This is in contrast to the timescale of the millions or billions of years during which the galaxies and their component stars in our universe have evolved. Singularly, the term is used for violent deep-sky events, such as supernovae, novae, dwarf nova outbursts, gamma-ray bursts, and tidal disruption events, as well as gravitational microlensing.^[1]

Time-domain astronomy also involves long-term studies of variable stars and their changes on the timescale of minutes to decades. Variability studied can be intrinsic, including periodic or semi-regular pulsating stars, young stellar objects, stars with outbursts, asteroseismology studies; or extrinsic, which results from eclipses (in binary stars, planetary transits), stellar rotation (in pulsars, spotted stars), or gravitational microlensing events.

Modern time-domain astronomy surveys often uses robotic telescopes, automatic classification of transient events, and rapid notification of interested people. Blink comparators have long been used to detect differences between two photographic plates, and image subtraction became more used when digital photography eased the normalization of pairs of images.^[2] Due to large fields of view required, the time-domain work involves storing and transferring a huge amount of data. This includes data mining techniques, classification, and the handling of heterogeneous data.^[3]

The importance of the time-domain astronomy was recognized in 2018 by German Astronomical Society by awarding a Karl Schwarzschild Medal to Andrzej Udalski for "pioneering contribution to the growth of a new field of astrophysics research, time-domain astronomy, which studies the variability of brightness and other parameters of objects in the universe in different time scales."^[4] Also the 2017 Dan David Prize was awarded to the three leading researchers in the field of time-domain astronomy: Neil Gehrels (Swift Gamma-Ray Burst Mission),^[5] Shrinivas Kulkarni (Palomar Transient Factory),^[6] Andrzej Udalski (Optical Gravitational Lensing Experiment).^[7]